The goal of this project is to identify specific morphological types of neurons in primates inner retina that contain the inhibitory transmitter gamma-aminobutyric acid (GABA), and to describe the neuronal circuitry of some of these cell types. The function of GABA in the retina is not well understood, but GABA has been implicated in visual perception of movement, form, and color. Two specific issues that will be addressed are (a) which classes of neurons (i.e.. bipolars, amacrines, ganglion cells) provide synaptic input to and receive synaptic output from newly- described GABA-immunoreactive cells that arborize in the nerve fiber layer, and (b) whether any ganglion cells contain significant levels of GABA. Intracellular dye injection will be combined with immunocytochemistry based on GABA antiserum or 3H-muscimol uptake followed by autoradiography to identify specific types of GABAergic neurons. Amacrine cell types will be characterized by somal size and position, dendritic arborization patterns, and level of branching in the inner piexiform layer. Retrograde fluorescent tracers will be combined with immunocytochemistry to determine whether any ganglion cells contain GABA. The synaptic connections of selected GABA-containing cell types will be examined with a combination of horseradish peroxidase injection and postembedding immunogold electron microscopy. The long-term objective of this study is to describe the projections and circuitry of GABAergic cells in the retina of macaque monkey to improve our understand- ing of normal retinal function in primates.